Sediments constitute the benthic environment, and play an important role in marine ecosystems. Various chemicals persist in sediments and can affect the benthic organisms. However, it has generally been difficult to identify specific toxicants that critically the effects in organisms. In the present study, we evaluated the toxicities of sediments collected from several sites in Japanese coastal areas, using fish embryos. As a result, some sediments induced embryo mortality and malformation in hatching larvae. We explored several approaches to facilitate the identification of causative chemicals based on biological responses in fish embryos. Hydrophobic extracts added into test water obtained from most sediments induced effects such as mortality and malformations in embryos. However, because hydrophilic extracts also affected embryos for a few sites, we could not distinguish the remarkable signatures based solely on the extract exposures. In addition, receptor activation by ligand-binding chemicals derived from these extracts―implicating xenobiotic metabolism, vitamin metabolism, and other pathways―was examined using the corresponding nuclear receptor target genes, and some genes changed at least partially with their effect-related factors. The approach of obtaining extracts followed by gene analysis, owing to its broad applicability, was suggested to be a potentially effective method for picking up candidate causative toxicants in sediments in the future.

Chronic toxicity tests (OECD TG 210 and 211) are now required for pesticide registration under the Agricultural Chemicals Regulation law in Japan. While Daphnia magna is typically sensitive to chemicals under limited food, the impact of differential feeding conditions in the TG 211 on EC_x values remains unclear. Therefore, we investigated whether the food amounts would affect the chronic toxicity (EC_x) of the reference substance (potassium dichromate). The D. magna reproduction test (OECD TG 211) specifies algal food (Chlorella vulgaris) levels at 0.1–0.2 mg C/daphnia/day. We performed the 21-day chronic reproduction tests under four groups separated by differential food amounts: 1) Overfeeding group (0.4 mg C/Daphnia/day); 2) Normal feeding group (0.2 mg C/Daphnia/day); 3) Changing amounts group (0.1 mg C/Daphnia/day for 1 week from the birth, then, 0.2 mg C/Daphnia/day for 2 weeks); 4) Minimum-feeding group (0.1 mg C/Daphnia/day). In group 4, the EC₁₀ and EC₂₀ values (based on the total reproduction of offsprings) were four to seven times lower than those in the other groups. Moreover, the total number of neonates did not met the criteria (≥60 neonates) in the control of group 4. At least 0.14 mg C/Daphnia/day of C. vulgaris is needed to produce 60 neonates. Although the feeding amount was within the recommended range, our study found that lower feeding amounts could cause unreliable EC_x value estimates. When interpreting chronic toxicity tests, we need to verify both guideline compliance and whether the conditions for EC_x calculations are met.

Cationic surfactants such as hexadecyltrimethylammonium salts (HTAC) are known to exhibit high toxicity to aquatic organisms; however, the extent to which water quality conditions influence their apparent toxicity has not been sufficiently clarified. In this study, we investigated the effects of selected water quality factors on algal growth inhibition by HTAC using the freshwater green alga Raphidocelis subcapitata. Algal growth inhibition tests were conducted using standard OECD medium and modified OECD media in which dissolved organic carbon (DOC), pH, hardness (Ca²⁺/Mg²⁺), or sodium concentration was independently adjusted. The results showed that algal growth inhibition by HTAC was significantly reduced under high-DOC conditions achieved by the addition of humic acid, compared with the standard OECD medium. In contrast, no significant effects of pH, water hardness, or sodium concentration on HTAC-induced growth inhibition were detected under the tested conditions. These findings suggest that the algal toxicity of HTAC is highly dependent on DOC concentration in the test medium, likely due to reduced bioavailability through sorption to organic matter. Consideration of DOC is therefore essential for reliable algal toxicity testing of HTAC.

In the European Union, a revised version of the “Guideline on Environmental Risk Assessment of Medicinal Products for Human Use” (EMEA/CHMP/SWP/4447/00) came into effect in September, 2024. This review explains the revised contents of the Guideline, summarizes points to note when conducting an environmental risk assessment, and proposes a useful project model for the pharmaceutical industry.